This invention relates to a method and an arrangement for injecting additives in oil products and the like during successive, separate loading or unloading operations on tank farms, in particular for filling of fuel to be transported by tank trucks.
On tank farms where fuel is filled for transportation with tank trucks there is blended into each batch or load additives to the main part of the tank contents, which may be an oil product such as gasoline or diesel oil. There is often the question of a specific additive prescribed by the various oil companies to which fuel is delivered from the tank farm concerned. It is very important to obtain an accurate dosage of additives to each individual batch, and this represents a great measuring and regulating problem, in particular because it is desired to stop the injection of additive before the outflow of the main product (the oil product) terminates. This is important in order to avoid unintentional transfer of remainders of additive from a preceeding batch for one tank truck to another batch in the next tank truck to be filled.
Previously there are known various methods for measured blending of two liquids, for example regulation of two constituents in connection with filling from regular gasoline pumps at gas stations. Examples of known solutions for such purposes are to be found in Norwegian patent No. 147.210 and British patents Nos. 1.438.164 and 1.474.019. These known methods take as a basis a first low octane type of gasoline and a second, high octane type of gasoline respectively. These are blended in various pre-determined ratios in order to obtain intermediate octane values. However, the known methods are not directed to the specific problem which the present invention aims at, namely correction of an inaccuracy or error incurred during a preceeding filling on a tank farm, for obtaining a more accurate blending ratio in a subsequent filling operation.